The objective of this project is to investigate the mechanism(s) of tetranitromethane (TNM) pulmonary toxicity and carcinogenicity. This project includes studies of the reactions of TNM with cellular DNA and proteins, in vitro and in vivo. In vitro reaction of TNM with DNA, or nucleosides revealed no evidence of DNA adducts when analyzed by HPLC. However, initial experiments using capillary electrophoresis show a number of potentially altered nucleosides resulting from reaction of TNM with DNA. Capillary electrophoresis is a considerably more sensitive method than HPLC. In vitro studies conducted to date have demonstrated that TNM does not appear to cause DNA strand breaks or DNA-protein adducts in A549 lung cells treated in vitro. Because TNM specifically nitrates tyrosine residues on proteins, the effects of TNM on phosphorylation and dephosphorylation of tyrosine, and subsequent effects on cell proliferation are being investigated. Because it is not currently feasible to conduct inhalation studies of TNM, intratracheal instillation studies were conducted to determine if this route of administration produces neoplastic lesions in the respiratory tract similar to those observed after inhalation exposure. Rats received a single instillation of one of five doses of TNM and subgroups sacrificed at 1, 4, 8, and 12 weeks to evaluate pulmonary lesions. Proliferative lesions were not observed in lungs of rats receiving a single instillation of TNM. The feasibility of administering multiple low doses of TNM is being investigated. This treatment regimen may reproduce the effects of vapor inhalation.